1. Field of the Invention
The present invention relates to a piston for an internal combustion engine, reinforced by casting a preformed member composed of a fiber reinforced material into a piston base material.
2. Description of the Related Art
Hitherto, with respect to the piston for the internal combustion engine such as a gasoline engine or a diesel engine, in order to improve combustion by optimizing gas flow, to make weight reduction, to improve fuel economy by ensuring a stroke, and to raise an acceleration performance and so forth, a crown portion of the piston has been developed so as to have a thin or reduced wall.
In the meantime, since the crown portion is directly subjected to combustion of air-fuel mixture, when the wall of the crown portion is thinned, countermeasures against a crack, meltdown, penetration, and the like are strongly required in order to maintain its strength and roundness against heat distortion caused by heat deflection.
In view of the above requirement, for example, Japanese Examined Patent Application Publication No. 7-86336 discloses the piston having a structure in which the strength of the crown portion (head portion) is increased by casting a steel skeleton member having a round core portion of the head portion, core portions of a pair of pin boss portions, skirt ribs, a skirt portion, and an engaging portion of a top ring integrally connected thereto into a light alloy base material (reinforcement material) and also, a heat dissipation effect is improved by thermal conduction to a cylinder or the like through the skeleton member of the piston.
Also, for example, Japanese Unexamined Patent Application Publication No. 11-285809 discloses the piston having a structure in which the strength of the piston is partially increased by casting a preformed member composed of a fiber reinforced material or the like into the base material of the piston.
However, when the steel skeleton member is casted in the base material of the piston as disclosed in the above-mentioned Japanese Examined Patent Application Publication No. 7-86336, there is a risk of an inadequate bonding strength between these different materials from each other.
As a countermeasure against the above-problem, there is a possibility of increasing the strength between the different materials from each other by forming the above-mentioned skeleton member with a preformed member. However, since the skeleton member disclosed in the above-mentioned Japanese Examined Patent Application Publication No. 7-86336 has a complicated structure for achieving a necessary stiffness and inhibiting thermal expansion, when the preformed member having such a complicated structure is casted, a flow of molten metal becomes complicated, as a result, the molten metal is impregnated less in the preformed member, thereby causing a risk of an inadequate strength of a part of the piston reinforced with a fiber reinforced metal of which the preformed member is composed.
In view of the above-mentioned problems, the present invention has been made. Accordingly, it is an object of the present invention to provide the piston for the internal combustion engine, achieving a necessary strength thereof and also inhibiting distortion of the crown portion while having a simple structure, even when the crown portion has a thin wall.